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# Water/Fuel Sensor: Resistance to Voltage Converter

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#### juicebiz

##### Newbie level 1
resistance to voltage converter

I want to monitor the water level in my RV tanks. There are resistance sensors available that have a float on a tube. When depending on where the float is on
the tube, the resistance is different. Here are some examples:

https://www.wemausa.com/tank_sensors/tank_level_sensors.htm#Fuel_Water_Tank_Sensors

I want to convert the resistance to a voltage 0 - 10 VDC and put it on a sensor in order to monitor it on my laptop using this software:

https://www.dataq.com/products/startkit/di194rs.htm

Any ideas about how to approach this is greatly appreciated.:|

water in fuel sensor

hi, I too want to make a water level controller.will you please tell me how these sensors work? Is it just like a variable resistor giving different ohms between two terminals depending upon the position of the float? THANKS. PRASHAR. prashbh@gmail.com

water in fuel sensor

You should double-check my suggestions before putting electronics near a fuel pump. Just be cautious and make sure there's no risk of getting a short circuit.

One method of getting a specific output voltage for a given resistance is to use a constant current source.
The basic concept is described on wikipedia: http://en.wikipedia.org/wiki/Current_source

I would recommend using the op-amp and transistor circuit pictured here: **broken link removed**

The website you provided has very little information, so I used this site as a reference for the pump's operating resistance:

assuming a 5.1v zener diode (**broken link removed**) you can use the following resistance values

for the sensor with a 0-180 ohm range the "sense" resistor should be a 910 ohm resistor
for the sensor with a 30-240 ohm range the sense resistor should be 120 ohms, however this sensor will not go all the way down to 0 volts

remember to avoid high voltage, the 12v car battery should be enough to power the circuit, or if you have to use a power jack plug in a 12v-15v adapter

in response to prashar's question of "how do these sensors work?" I suggest reading the wikipedia entry on level sensors
http://en.wikipedia.org/wiki/Level_sensor

I would expect a fuel sensor to be a pneumatic sensor. In this case basically the shaft contains a bubble which exerts pressure on the top based on how deeply it is immersed. This allows the electronics to be mounted outside fuel tank to reduce risk of electrically igniting the fuel.

resistance to voltage

Appolgies for bringing this old post up, but it almost exacly describes what i have been trying to do for ages.

i have two types of thermistor the spec sheets can be found below. i need to generate a 0-5v signal from the output of the resistors. i would like to be able to use as much of the 0-5v range as possible to keep resolution has high as possible. inverted ouput is not a problem i can configure my equipment to work either with 0v being low temp & 5v high temp or 5v low temp & 0v high temp.

With both sensors i am really only concerned with temperatures above -10c giving a range of 57 ohm to 9397 ohm for the NTC_M12-H and 71 ohm to 9397 ohm for the NTC_M12-L

If someone could advise on the correct changes to the values for the sense resistor and any other components i would be very gratefull.

resistance to voltage circuit

The said "float-on-a-tube" sensors are using a reed switches connected to a resistor chain and a magnetic float rather than NTC.

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